It is known in the art relating to chain drives to use chain guides and tensioners to control undesired lateral chain motion and to hold the chain on the drive and driven sprockets. A new chain as installed may have a minimum of slack so that it is not likely to skip a sprocket tooth in operation. However, during long service, the chain length increases, requiring the tensioner to take up the slack to prevent tooth skipping.
In one tensioner design, the tensioner includes a ratcheting stop cam and a plunger having an external plunger rack. The plunger rack includes teeth, which the cam engages to act as a stop against retracting motions of the plunger. The pitch of the ratchet in the tensioner is set to allow a small, given tensioner backlash to prevent worn (i.e., long) chains from skipping on a sprocket. On the other hand, we have found that when a new chain is still short and taut, the chain dynamics may cause the tensioner stop cam to advance an extra ratchet tooth too soon. This condition can cause increased chain tension and resulting “chain whine” noise. Worn chains run quieter for whine, so the tensioner advancing an extra tooth (i.e., over-ratcheting) does not lead to a whine issue.